There is a need to synchronize a plurality of clocks accurately.
For example, in factory automation (FA), there is a case where one control apparatus controls a plurality of machine tools via a network. In order to realize highly accurate control, the plurality of machine tools are controlled based on time point information. For example, a motor for X-axis movement and a motor for Y-axis movement are started to rotate at the same time point at the same rotation frequency, so that a straight trajectory is drawn. If any one motor starts to rotate with a delay, the trajectory forms an angle, and a straight trajectory cannot be drawn. For this reason, the time points of the plurality of machine tools need to coincide to each other via the network.
The time interval taken for propagation of communication via the network is not constant. For example, due to fluctuation of the relay delay time interval of a relay device or fluctuation of the propagation speed of a cable, the propagation time interval is different each time. This makes it difficult to synchronize the time via the network. As a technique that suppresses the influence of the fluctuation of the propagation time interval and calculates the difference (quartz deviation ratio) among clock speeds that results from an error and the like of the quartz oscillation frequency, for example, Patent Literature 1 is available.